Image capture devices such as digital cameras have become very popular due in part to a reduction in production costs, increase in overall quality, and particularly because camera functionality is being embedded into other electronic consumer devices such as cellular telephones and personal digital assistants (PDAs).
Image blur due to unsteady hand movement or the like during an image capture operation is often difficult to avoid for the inexperienced photographer or a user with an unsteady hand. Blur in an image is frustrating, as it detracts from the appeal of the image. With standard auto-exposure functions in image capture devices, low-light conditions are compensated for by lowering the shutter speed of the image capture devices, thereby increasing the exposure time in order to capture a bright enough image. This increase in exposure time increases the likelihood that movement will occur during the exposure time, thus increasing the likelihood of blur in the captured image. The same blur situation may arise if high-speed image capture device movement occurs during image capture, where the exposure time is normal.
Methods for post-processing a captured image to remove blur are known. These methods typically involve measuring the extent of blur in the captured image, and correcting for the measured blur. However, under very low-light and/or very high speed conditions that cause extensive blur, the extent of the blur can be so great that such post-processing cannot restore the image.
U.S. Pat. No. 6,778,210 to Sugahara et al. discloses a system that limits exposure time in a digital camera to keep blur within allowable or undetectable limits. The exposure time is adjusted based on the physical dimensions of the camera, on the basis that image blur relative to the imaging frame is inversely proportional to frame size and focal length. According to the Sugahara et al. method, in the event that the total manual or photometrically set exposure time exceeds the exposure time limit for acceptable blur, the camera is set to take a series of limited exposure images (their respective exposure times adding up to the total exposure time) by controlling the accumulation times of the image pickups. The images are subsequently processed for respective motion, correlated, and the motion is corrected. Each resultant image contains acceptable levels of blur, and results in an output image having an acceptable level of blur. One disclosed system recognizes reduced signal levels due to short exposure time and employs a velocity sensor instead of a motion correlation algorithm in order to quantify the motion.
U.S. Patent Application Publication No. 2004/0239771 to Habe discloses a method for controlling image blur quantity by adjusting the ISO speed setting of a digital camera. Prior to image capture, the camera in a blur prevention mode engages a vibration detector to, along with a known shutter speed and focal length, calculate a blur quantity. If the calculated blur quantity is greater than a predefined limit, the ISO speed of the camera is shifted to higher sensitivity by an extent that it is based on the ratio of calculated blur to the predetermined blur limit. In doing so, the aperture (i.e., field depth) is not changed. The method retains image quality by basing the adjustment of ISO speed on the image blur quantity, rather than on the shutter speed. While the ISO speed may be raised, it may also be lowered to gain higher-quality images having increased blur that it is within acceptable limits.
While blur correction algorithms, and blur reduction and limiting methods are known, improvements are of course desirable. It is therefore an object to provide a method, apparatus and image capture device for limiting motion blur during image capture.